Variable font character generator



United States Patent 3,422,737 VARIABLE FONT CHARACTER GENERATOR John M. Bailey, Jr., Fairport, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Dec. 27, 1965, Ser. No. 516,393 U.S. Cl. 95-45 4 Claims Int. Cl. B411) 13/00, 19/00, 23/ 00 This invention relates generally to character generators and more specifically to those character generators which incorporate provisions for changing or varying the character fonts utilized therein.

In order to attain those degrees of writing speed deemed necessary to cope with the so-called information explosion of recent decades, the graphic communications industry has looked increasingly toward electro-optical character generators as the only logical alternative to inertia-limited mechanical printing systems. Yet the very profusion with which such generators have been proposed and constructed points up a basic problem that continues to beset their designers. Succinctly stated, this problem has been an absence of versatility in the printout capabilities of individual devices: We refer particularly here to the electro-optical devices ability-or perhaps more accurately stated, lack of abilityto graphically depict alphanumeric information with the same full variety of type forms, shapes, and sizes that one can readily achieve with a fully serviced mechanical printer.

Some examination of the myraid character generators of the prior art will demonstrate that these devices have generally been less than satisfactory in such respect for one of two reasons. In particular where such devices were simple enough to make their cost of production reasonable, they could not achieve the sophistication that versatility implied. Such devices, for example, might utilize a spot of light in combination with a mechanical stencil to produce the characters on a screen or the like. The stencil could, of course, be more sophisticated in nature than a mere defined passage, and might by way of illustrating a full system take the relatively involved form of electro-optical light valves positioned to selectively expose sections of a stencil together with complex optics to position and align individual characters.

But regardless of the means employed to illuminate the stencil, it is unfortunately true that the variety of characters obtainable remains a function of the particular stencil utilized and there is no simple or rapid manner to varymuch less change-these stencils.

On the other hand the prior art does show that one may achieve more sophistication and variation in production of characters where one utilizes a more nearly pure electronics approach for generation. A typical approach here utilizes a cathode ray tube as the light surface for display of the characters, and thus in one way or another directly generates the characters on the tube face. Even though these systems are-as would be expectedquite complex, they still do not provide satisfactorily for variations and/or interchangeability in the character fonts utilized. In those few instances where variation is provided it is usually only of slight degree and for such purposes necessitates the use of complex and expensive 'banks of memory cores and switching network for storing and withdrawing the signals corresponding to a given character in a font.

In accordance with the foregoing it is an object of the present invention to provide an electro-optical character generator in which complete changes of character fonts may be achieved by purely electronic means and in a minimum of time.

It is another object of the present invention to provide a variable font electro-optical character generator in which character fonts are so stored and utilized that only one bit at a time need be withdrawn from the storage means, thereby enormously simplifying the memory system.

It is a further object of the present invention to provide a character storage technique that lends itself to rapid variations and changes in the characters stored while at the same time permitting extreme case in character decoding.

It is a still further object of the present invention to provide an electronic character generation technique of great flexibility and adaptability, but utilizing relatively simple and inexpensive components.

It is yet a further object of the present invention to provide a character generator in which alphanumeric information of enormous variety may be readily displayed at the direction of a proximate or remote digital computer.

In the present invention these and other objects are achieved by means of a generating system including a cathode ray tube which is utilized in conjunction with suitable optics as a light writing source for a spaced photoreceptor, which in a preferred embodiment may comprise a sensitized xerographic drum. Under the control of input logic which may constitute a proximate or remote computer, the decoder-storage portion of the generator is initially loaded with an appropriate encoded character library. The character library is in effect loaded into a specially organized recirculating delay line and thereafter continues to cyclically recirculate within this line. Subsequently, at the instance of control exercised by the input logic, successive bits may be gated out from the recirculating delay line to serially blank or unblank the CRT (cathode ray tube) spot as the spot sweeps a predetermined pattern. The resulting alphanumeric pattern is imaged in real time on a sensitized xerographic drum and after development transferred to a paper surface or the like in accordance with standard xerographic practice.

A more complete understanding of the present invention, of its numerous advantages, and of the manner in which the invention acts to obtain the several objects previously recited and other objects not explicitly indicated, may now best be gained by a reading of the following detailed specification together with an examination of the drawings appended hereto in which;

FIG. 1 is an electronics block diagram for the overall character generator;

FIG. 2 is a diagrammatic illustration of the delay line organization; and

FIG. 3 diagrammatically illustrates a typical scan pattern utilized in association with the present device.

In the description that follows certain parameters will frequently be assigned to data being manipulated by the character generator. Thus, for example, a word may be referred to as comprising a specific number of bits or a portion of the delay line may be described as having a given specific number of bits reserved for a given purpose, etc. In all instances such as these it is to be understood that the parameters cited are intended merely to concretely illustrated operation of the system and are not in any way intended to delimit the invention otherwise described.

In the electronics block diagram depicted in FIG. 1, digitally encoded data is fed to and from the decoderstorage section 3 of the character generator by the input logic at 1. The latter provides, in a stream which will be shown to be appropriate for the system, all the digitally encoded loading data utilized in generation, and also provides the encoded character data that subsequently initiates and controls generation of the characters. The input logic 1 may well compiise a digital computer and need not in fact be in close proximity to the remainder of the system. Thus, for example, the input logic could include a remote digital computer connected to a proximate data set interface by standard telephone transmission lines and a standard dataphone. The relative proximity of the input logic is not significant to the operation of the system except to the extent that where telephone lines intervene the data flow rate is necessarily limited by the capabilities of these transmission lines.

At the direction of the input logic 1, data assumed initiating at this logic and representing a character font, is loaded through the load logic 2 into the delay line 4. The precise Sequence in which the data is loaded is significant to the invention and will be more fully explained below; however, once the loading process is completed the generator is ready for character production in accordance with encoded words thereafter originating at input logic 1 and routed to the write logic 5.

The decoding action of the elements contained within decoder storage section 3 is such as to convert a relatively low bit encoded character into a serial stream of considerably more numerous bits which are then used to blank or unblank the electron beam of CRT 15 as it scans a prescribed path. Typically a 7 bit encoded character (contained in say a 10 bit transmitted word) is so converted into a serial stream of 84 bits. Essentially, the decoder consists of the recirculating delay line 4 whichpurely for purposes of illustration-may be considered as a 5 miliisecond magnetostrictive delay line capable of storing 10,000 NRZ (non-return to zero) hits at a clock rate of 2 mc./s. These figures are arbitrary to the invention but are designated to illustrate the parameters that might be chosen where an intervening telephone line in the input logic is assumed to limit the input data flow rate to some 2,000 bits per second. During the loading process timing circuits functionally contained within load logic 2 gate the incoming encoded data into the recirculating delay line 4 in proper time sequence.

A graphic depiction of the organization of the loaded delay line 4 is shown in FIGURE 2. In order to fully appreciate the operation of the decoder, one may assume an arbitrary cyclic recirculation of the data in the delay line in a direction corresponding to the arrow in FIGURE 2. This is to say that one may consider the various signals propagating in the delay line 4 to consecutively and cyclically pass a given fixed point external to the delay line, such as point 44. The delay line is organized during loading with an initial section, such as 45, illustratively shown as containing 128 bits, which acts as a synchronization Word to indicate the reference point after which the encoding data will start. During the loading mode the sync bits contained in section 45 are loaded into the delay line in the same manner as the character encoding data.

Following this sync segment, a series of successive segments, such as 46, are loaded into the delay line. Consistent with the examples thus far cited, we may consider specifically that 84 such successive segments are loaded into the line. Thus in FIGURE 2, the second such segment is identified as 47, intermediate (but unshown) segments are indicated by the dotted lines at 48, and the final-or 84th segment-is conveniently identified as 49. Each of the successive segments 46, 47 and so forth is broken up into as many hits as corresponds to the number of characters used in a character set. In FIGURE 2, for example, it may be illustratively assumed that each of the segments 46, 47 and so forth, is broken up into 110 such bits. The order in which these bits are located within each particular segment corresponds to the code which represents the character. For example, if ASCII is used (the reference here is to the American Standard Code for Interchange of Information recommended by the IEEE) the 65th bit in the segment 46, which is identified in FIGURE 2 by the numeral 465, will be the first bit required to display the character A. Similarly, the 65th bit in segment 47, which is therein identified by the numeral 5, l be the second bit required to display the character A, and so forth, until finally the 84th segment of bits is reached wherein again the 65th bit, identified in FIGURE 2 by the numeral 495, represents the 84th bit required to display the same character.

At 50 a final segment, spatially adequate for an unspecified number of bits, is provided. This segment is not utilized operationally but is rather reserved to provide extra space in the event the character font is increased numerically. The manner in which the organized delay line is utilized to achieve character generation may now be set forth. More particularly, encoded characters originating at input logic 1 are routed to the decoder-storage portion of the generator and are compared to the state of a counter within the write logic 5 which keeps a count of the data bits in the delay line following the sync segment 45. Whenever a match exists-which will occur once in every segmentthe bit is gated out of the delay line 4 by the write logic and is held at the beam modulator 10 while blanking or unblanking the CRT 15 beam depending upon its binary value. If the scan time of a fixed pattern on CRT 15 is made approximately identical with the time required for all 84 segments (45, 46, etc.) to pass a fixed point in the delay line, it follows that exactly M of the scan time after an initial bit is gated out, the following bit value of the same character will be detected, gated out, and will thereupon replace the previous bit in modulating the CRT electron beam. This scheme of encoding thus allows serial character decoding with only one bit stored external to the delay line. Additionally it may be noted that where as previously suggested a full delay line recirculation period occupies 5 ms., it follows that the recirculation period will exactly match the period of one ten bit input word for the exemplified input rate of 2,000 bits per second. Therefore once during every word period of 5 ms., every bit in the delay line will be exposed to comparison with the input code and all 84 bits comprising the particular character will be gated out during this period.

The write logic 5 in addition to providing appropriate data manipulation signals in response to the encoded character generating data transferred from input logic 1 also generates the required scan start-stop signals for the pattern generator 6. Characters and symbols are generated on the face of CRT 15 by modulation of the electron beam as it is deflected, under control of pattern generator 6, through a fixed line pattern. This pattern, illustratively shown in FIG. 3, is repeated for each character or symbol. The total scan timeas has been previously discussedis arranged to be slightly less than the circulation period of the delay line 4, so that the scanning beam can be appropriately blanked by the serial bit data stream from the decoder-storage section 3. With the parameters as previously indicated the 84 bits-which are evenly spaced in time through the scan period-switch the beam on or off in accordance with their binary value. For example, a binary one" would generate a visible stroke for a period which approximately equals & of the character scan time.

The pattern generator 6 is seen to act through the X and Y deflection amplifiers at 7 and 8 respectively. The latter are desirably direct-coupled feed-back amplifiers. They provide a low impedance drive to the deflection yoke 9 for accurate positioning of the electron beam. The deflection yoke 9 used in conjunction with the CRT is a standard unit and typically is a single ended unit of flat field characteristics exhibiting a spot recovery time of the order of four microseconds.

In the overall generator the initial position of the first character formed on the face of CRT 15 is controlled through the use of initial beam positioning circuits contained within pattern generator 6 and controlled by input logic 1. Upon the completion of one character, the pattern generator circuitry skips the electron beam to the scan-start position of the following character. This introduced a spacing between characters. When the skipping of spaces is desired the input logic is programmed to send the generator a character code which has been previously encoded and entered into the recirculating delay line as a complete blank. That is to say, the CRT beam is blanked throughout the scan period.

In a typical format 80 character spaces are generated in a CRT line before another line is initiated. Each such line is imaged through conventional optics 16 upon the photoreceptor 17. The latter may most conveniently take the form of a sensitized xerographic drum rotatable about an axis transverse to the axis of CRT 15. Assuming in FIG. 1 that the photoreceptor does take such form, an indexer is provided at 18 for advancing the drum stepwise one line at the completion of each transverse line of characters. It may be noted that this index is in electrical connection with input logic 1, the latter supplying signals to actuate the indexing operation. Charge sensitization means for the drum are not shown but are completely conventional. Neither are development means or means for transferring the developed latent electrostatic image to paper or the like shown since these subsequent xerographic techniques are fully described in numerous places and are considered completely obvious to those skilled in this art.

It will be readily appreciated by those skilled in the art that the character generating capabilities of the present system are in no way limited to the photoreceptor printout type of unit being particularly considered herein. This is to say that the character generation technique described is, on the contrary, a generalized scheme that may be readily seen to have the widest applications. That technique is seen to include the concept of organizing a delay line into successive, and in turn sub-organized, segments. Thereafter character generation is achieved by serially gating out successive corresponding bits in the successive segments, as such segments cyclically circulate in a closed loop.

It is of particular importance here to realize that the makeup of the recirculating delay line 4that is to say its organization-may be completely changed in an extremely short period. Considering for example the presently described device, it is evident that the organization of the delay line-which in effect means the character font loaded in the line-may be completely changed in the order of four and one-half seconds even in such instances where data flow is limited by telephone transmission lines to 2,000 bits per second. In a more general case (where loading data is available locally) the loading of the delay line will be time limited only by the recirculation period of the line itself. Thus we could be describing a complete change of the character font therein contained within a time period of the order of milliseconds.

It will of course be further evident that character fonts of any description whatsoever could be loaded into the delay line. Thus, for example, one might in the reloading period wish to change from the Latin alphabet to the Cyrillic alphabet, or to Arabic characters or so forth. Similarly the line could be reloaded with mathematical symbols, designations and so forth.

While the present invention has been particularly described in terms of a specific embodiment thereof, it will be understood that in view of the foregoing specification numerous deviations therefrom and modifications thereupon may be readily devised by those skilled in the art without yet departing from the present teaching. Thus, for example, while the present generator has been particularly described as utilizing a recirculating delay line, it will be readily understood that the latter is merely one number of a class of such recirculating memory devices, and that other members of such class could be substituted in the generator and function in an equivalent manner. Accordingly, the present invention is to be broadly construed and limited only by the scope and spirit of the claims now appended hereto.

What is claimed is:

1. In a reproduction apparatus having optical means for imaging light patterns from a cathode ray tube onto an electrostatic means, whereby a latent developable image may be formed upon said electrostatic means for subsequent development and reproduction of said light patterns, the improved apparatus including a variable font character generator, said character generator comprising input logic means;

recirculating decoder-storage means adapted for storing encoded character fonts transmitted from said input logic means, said recirculating decoder-storage means being further adapted to respond to encoded signals representative of said stored encoded characters and presented to said recirculating decoder-storage means by selectively gating out electrical signals indicative of the characters corresponding to said encoded signals;

pattern generator means electrically connected to said decoder-storage means and said cathode ray tube, said pattern generator means including circuitry for establishing a fixed scan pattern on the face of said cathode ray tube, said pattern generator means further including circuit means for intensity modulating said scan pattern in accord with said electrical signals from said decoder-storage means whereby light patterns may be formed upon said cathode ray tube representative of said characters.

2. Apparatus according to claim 1 wherein said decoder-storage means comprises a serially organized recirculating delay line, load logic means, and write logic means, said load logic means being electrically positioned and adapted to serially load successive digitally organized segments into said delay line from said input logic, individual bits in each of said segments being thereby positioned at assigned points in the said segment corresponding to a given character in the said font, correspondingly positioned bits in successive segments having binary state values in accord with those necessary to blank or unblank said fixed scan pattern on the face of said cathode ray tube when said values are 'made to intensity modulate said pattern in synchronization with said scan, said delay line being adapted to cyclically recirculate said segments, said write logic being electrically positioned and adapted to gate out from said delay line a series of binary state valued signals identical to those stored in said delay line at said identical assigned points in said successive segments upon receipt from said input logic of the said encoded signal representative of the character to which the said assigned points correspond.

3. A variable font character generator comprising a cathode ray tube for displaying light patterns on the face thereof,

input logic means for generating encoded character font signals, recirculating decoder-storage means for storing said encoded character font signals received from said input logic means, said recirculating decoder-storage means responding to said encoded signals representative of said stored encoded characters and presented to said recirculating decoder-storage means by selectively gating out electrical signals indicative of the characters corresponding to said encoded signals, and

pattern generator means electrically connected to said decoderstorage means and said cathode ray tube for establishing a fixed scan pattern on the face of said cathode ray tube, said pattern generator means further including circuit means for intensity modulating said scan pattern in accordance with said electrical signals from said decoder-storage means whereby light patterns may be formed upon said cathode ray tube representative of said characters.

4. Apparatus according to claim 3 wherein said decoder-storage means comprises a serially organized recirculatin delay line, load logic means, and write logic means, said load logic means being electrically positioned and adapted to serially load successive digitally organized segments into said delay line from said input logic, individual bits in each of said segments being thereby positioned at assigned points in the said segment corresponding to a given character in the said font, correspondingly positioned bits in successive segments having binary state values in accord With those necessary to blank or unblank said fixed scan pattern on the face of said cathode ray tube when said values are made to intensity modulate said pattern in synchronization with said scan, said delay line being adapted to cyclically recirculate said segments, said Write logic being electrically positioned and adapted to gate out from said delay line a series of binary state valued signals identical to those stored in said delay line at said identical assigned points in said successive segments upon receipt from said input logic of the said encoded signal representative of the character to which the said assigned points correspond.

References Cited UNITED STATES PATENTS JOHN M. HORAN, Primary Examiner. 

1. IN A REPRODUCTION APPARATUS HAVING OPTICAL MEANS FOR IMAGING LIGHT PATTERNS FROM A CATHODE RAY TUBE ONTO AN ELECTROSTATIC MEANS, WHEREBY A LATENT DEVELOPABLE IMAGE MAY BE FORMED UPON SAID ELECTROSTATIC MEANS FOR SUBSEQUENT DEVELOPMENT AND REPRODUCTION OF SAID LIGHT PATTERNS, THE IMPROVED APPARATUS INCLUDING A VARIABLE FONT CHARACTER GENERATOR, SAID CHARACTER GENERATOR COMPRISING INPUT LOGIC MEANS; RECIRCULATING DECODER-STORAGE MEANS ADAPTED FOR STORING ENCODED CHARACTER FONTS TRANSMITTED FROM SAID INPUT LOGIC MEANS, SAID RECIRCULATING DECODER-STORAGE MEANS BEING FURTHER ADAPTED TO RESPOND TO ENCODED SIGNALS REPRESENTATIVE OF SAID STORED ENCODED CHARACTERS AND PRESENTED TO SAID RECIRCULATING DECODER-STORAGE MEANS BY SELECTIVELY GATING OUT ELECTRICAL SIGNALS INDICATIVE OF THE CHARACTERS CORRESPONDING TO SAID ENCODED SIGNALS; PATTERN GENERATOR MEANS ELECTRICALLY CONNECTED TO SAID DECODER-STORAGE MEANS AND SAID CATHODE RAY TUBE, SAID PATTERN GENERATOR MEANS INCLUDING CIRCUITRY FOR ESTABLISHING A FIXED SCAN PATTERN ON THE FACE OF SAID CATHODE RAY TUBE, SAID PATTERN GENERATOR MEANS FURTHER INCLUDING CIRCUIT MEANS FOR INTENSITY MODULATING SAID SCAN PATTERN IN ACCORD WITH SAID ELECTRICAL SIGNALS FROM SAID DECODER-STORAGE MEANS WHEREBY LIGHT PATTERNS MAY BE FORMED UPON SAID CATHODE RAY TUBE REPRESENTATIVE OF SAID CHARACTERS. 